Recently, a large number of measurements using intermolecular interactions such as immune responses are being carried out in clinical tests, etc. However, since conventional methods require complicated operations or labeling substances, several techniques are used that are capable of detecting the change in the binding amount of a test substance with high sensitivity without using such labeling substances. Examples of such a technique may include a surface plasmon resonance (SPR) measurement technique, a quartz crystal microbalance (QCM) measurement technique, and a measurement technique of using functional surfaces ranging from gold colloid particles to ultra-fine particles. The SPR measurement technique is a method of measuring changes in the refractive index near an organic functional film attached to the metal film of a chip by measuring a peak shift in the wavelength of reflected light, or changes in amounts of reflected light in a certain wavelength, so as to detect adsorption and desorption occurring near the surface. The QCM measurement technique is a technique of detecting adsorbed or desorbed mass at the ng level, using a change in frequency of a crystal due to adsorption or desorption of a substance on gold electrodes of a quartz crystal (device). In addition, the ultra-fine particle surface (nm level) of gold is functionalized, and physiologically active substances are immobilized thereon. Thus, a reaction to recognize specificity among physiologically active substances is carried out, thereby detecting a substance associated with a living organism from sedimentation of gold fine particles or sequences.
In all of the above-described techniques, the surface where a physiologically active substance is immobilized is important. Surface plasmon resonance (SPR), which is most commonly used in this technical field, will be described below as an example.
A commonly used measurement chip comprises a transparent substrate (e.g., glass), an evaporated metal film, and a thin film having thereon a functional group capable of immobilizing a physiologically active substance. The measurement chip immobilizes the physiologically active substance on the metal surface via the functional group. A specific binding reaction between the physiological active substance and a test substance is measured, so as to analyze an interaction between biomolecules.
Japanese Patent No. 2815120 discloses a surface to which a hydrogel matrix is bound via a compound forming a self-assembled monolayer (SAM compound), as an example of a detection surface having a functional group capable of immobilizing a physiologically active substance. Specifically, a layer comprising 16-mercaptohexadecanol binds to a gold film, resulting in the formation of a barrier layer. On the gold film, a hydroxyl group of the barrier layer is treated with epichlorohydrin so as to be epoxy-activated. In the subsequent step, dextran is allowed to bind to the barrier layer via an ether bond. Then, bromoacetic acid is allowed to react with a dextran matrix, resulting in introduction of a carboxymethyl group.
However, the mass production of sensors with the use of the SAM compound having a carbon chain with a carbon number of 10 or more described in Japanese Patent No. 2815120 involves the following problems: (1) it is necessary to use a large amount of a solvent for the formation of a film because of the insolubility of SAM compounds, resulting in increased burdens on the global environment, and leading to concerns regarding the health of production workers; (2) the starting materials are not widely distributed, and thus many steps are required for synthesizing such compound, resulting in high costs and difficulties in terms of supply; and (3) denaturation of plastic is likely to be caused when a sensor substrate is made of plastic.